Cleans up the public exports for the package itself:
* `parseFunctions()` was only used in playground, so this moves the definition
there. I had to update playground's dependencies to ensure the babel version
matched.
* Flattens away the `HIR` const in the export, and exports just 4 functions all
at the top-level: `run()`, `compile()`, `printHIR()`, and
`printReactiveFunction()`.
This will make it very easy to split the core compiler into a separate package
from the babel plugin, though i'm not sure it's worth doing that (yet).